The invention relates to a method for producing a secondary lithium cell which has at least one carbon-containing negative electrode, at least one lithium-intercalating positive electrode, at least one separator disposed between the positive and the negative electrode, and a nonaqueous lithium ion-conducting electrolyte.
Electrochemical cells having a high energy storage capacity use safety precautions which, e.g. in the case of short circuits, provide protection against spontaneous release of energy stored therein. To this end, it has previously been proposed to integrate a heat-sensitive protective mechanism into lithium ion cells which is designed, beyond a predefined cell temperature, to block or at least significantly limit the ion flow in the cell.
U.S. Pat. No. 4,075,400 discloses a separator which includes an agent that poisons the electrochemical cell reaction, is embedded into a temperature-sensitive material and released beyond a predefined temperature.
U.S. Pat. Nos. 4,650,730 and 4,73 1,304 disclose separators comprising two microporous layers having different melting points. When the melting point of the low-melting material is reached, the latter loses its porous structure and, thus, reduces ion flow in the cell.
U.S. Pat. No. 4,741,979 describes a separator which is made of wax-coated fibers. The wax is designed to melt beyond a predefined temperature and seal the pores between the fibers.
U.S. Pat. No. 5,091,272 further discloses a separator for electrochemical cells, which involves polymer particles having a predefined melting temperature being applied to the separator. The application of the polymer particles according to ""272 takes place from a dispersion of the polymer particles in a low-boiling solvent. Particles having a size of from about 1 to 15 xcexcm are applied to the separator in layer thicknesses of about 25 xcexcm with the aid of binders. The application from a low-boiling solvent does, for environmental reasons, require complicated equipment to remove the solvent vapors from the waste air, and the binders remaining in the cell may adversely affect the electrochemical reactions of the cell.
It is an object of the invention to specify a method which simplifies the production of electrochemical cells having a heat-sensitive protective mechanism, does not lead to the introduction of materials which, during normal operation, affect the electrochemistry, and shortens the response times to activate the interruption in the ion flow in the electrochemical cell.
The invention relates to lithium ion batteries having carbon-containing negative electrodes.
The invention particularly relates to a method for producing a secondary lithium cell having a heat-sensitive protective mechanism in such a way that the electrodes and/or the separator are coated, by means of electrostatic powder coating, with wax particles which are insoluble in the electrolyte, have a melting temperature of from about 50 to about 150xc2x0 C. and a mean particle size of from about 6 to about 20 xcexcm, the amount of wax being between about 0.5 and about 2.5 mg/cm2 of electrode area.